The present invention relates to a method for measuring the remaining time of tape in a tape recorder, and more particularly, to a method for correctly measuring the remaining time of tape even when the tape runs at a high speed or the speed of tape changes.
A known tape recorder exercises a function of displaying the remaining time of running tape continuously when the tape is driven. In the case of DAT(Digital Audio Tape Recorder), for example, the tape runs regularly at a speed of V.sub.t =8.15 m/s when driven by a capstan motor at a normal speed. So, when one period is measured with the reel pulse of a supply reel by a microcomputer, the remaining time(R.sub.t) can be found as a theoretical value according to the following formula. EQU R.sub.t =[(V.sub.t T.sub.s).sup.2 -(2.pi.r.sub.o).sup.2 ]/4.pi..delta.V.sub.t ( 1)
wherein,
V.sub.t : Running speed of tape when tape runs at normal speed PA1 T.sub.s : One period of supply reel PA1 .delta.: Thickness of tape PA1 r.sub.o : Radius of hub PA1 (a) judging whether the present remaining time is calculated; PA1 (b) measuring one rotation period on the part of the supply reel by the microcomputer in the case of normal speed running mode in response to the result of a judgment formed in the above step(a); PA1 (c) finding one new rotation period by subtracting a certain quantity of change in the one rotation period from or adding it to the just previous rotation period according to the running direction after every one rotation period of reel passes away in a condition where the remaining time is calculated in the case of high speed running mode or in the case of speed-changing mode in response to the result of a judgment formed in the above step(a); and PA1 (d) recording the new remaining time by subtracting the value corresponding to the one new rotation period from or adding the value corresponding to the one new rotation period to the remaining time of running tape already inputted in the above step(a) according to the direction of running every time tape effects one periodic rotation.
Consequently, when the tape runs at normal speed, the remaining time found according to the above formula(1) is increased or decreased by the timer of a microcomputer.
In the case where the tape is made to run at normal speed by the capstan motor, running speed(V.sub.t) of the tape is constant and the remaining time can be correctly increased or decreased. In the case where the tape runs at high speed mode, the remaining time cannot be increased or decreased correctly for the reason that it is made to turn around fast by driving the reel motor directly, and running speed of the tape is inconstant depending on the remains of tape wound to the reel.
Thus, conventional DAT causes a problem in that the remaining time cannot be displayed correctly on the display screen in the case of high speed running mode and the remaining time must be calculated again when the tape is shifted to normal speed-running mode from high-speed running mode.